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Purpose: The aim of this study was to examine the long-term impacts of mechanical compaction and cultivation on soil C and N pools, δ13C and δ15N of soil and foliage as well as tree growth. Materials and methods: In a hoop pine plantation of subtropical Australia, the diameter at breast height over bark (DBHoB) and tree height; δ13C and δ15N of soil and foliage; and soil C and N pools were determined after 17 years following forwarder compaction (control, light and heavy) and cultivation (control and disc plough) treatments. Results and discussion: Light compaction was associated with the significantly higher soil total carbon (TC) and total nitrogen (TN) in the 20–30 cm soil and higher TN in the 30–60 cm soil (p < 0.01). Cultivation was linked to the significantly higher soil TC in the 0–10 cm soil, and TC, TN and hot water-extractable total nitrogen (HWETN) in the 10–20 cm soil (p < 0.01). Higher δ15N in the 0–10 cm soil and in the foliage in the heavily compacted plots was due to previous soil denitrification, while light compaction and cultivation were associated with the lower foliar δ13C due to decreased foliar N concentration and reduced photosynthesis rate with increasing foliar biomass under higher N supply. Conclusion: The δ13C and δ15N of foliage and soil were useful indicators of the C and N processes in plant-soil system in response of management impacts in the plantation. Light compaction and cultivation generally had beneficial impacts on soil C and N pools over long term, whereas there was no difference in the impacts of different compaction and cultivation treatments on tree growth. [ABSTRACT FROM AUTHOR]

Purpose: This study examined the usefulness of 15N natural abundance (δ15N) with in situ core incubation to quantify the predominant N transformation processes in a natural suburban forest of subtropical Australia, which was subjected to prescribed burning. Materials and methods: In situ core incubation for 3 days with 20 ml water, or 160.79 ml of 60 mg L−1 NO3−-N surface application, and in situ core with 160.79 ml water but without incubation were set up in Toohey forest for sampling three times as before (once) and after (twice) a prescribed burning. The δ15N of NH4+-N and NO3−-N in the top 5 cm soil before and after the incubation, and δ15N of NO3−-N in the 5–10 cm soil before incubation were compared with each other to examine the soil N mineralisation, nitrification, denitrification, and nitrate leaching processes. Results and discussion: The significant decrease in δ15N of NH4+-N after incubation under 20 ml water treatment was ascribed to soil N mineralisation, and the significant decrease in δ15N of NH4+-N and significant increase in δ15N of NO3−-N after incubation with elevated water and nitrate inputs were associated with N mineralisation and nitrification, respectively, 2 months after the burning. The 160.79 ml water treatment also triggered nitrification in the baseline soil cores in both samplings after the burning. Water was crucial to stimulate soil N mineralisation and nitrification, but excessive water depleted labile N pools and reduced N mineralisation and nitrification. Burning effects were hard to separate from the seasonal impacts on soil N cycling processes. Conclusions: The δ15N in soil mineral N pools was sensitive to indicate soil N mineralisation and nitrification processes. Soil water and labile N were determining factors for N transformations in the soil. It is suggested that δ15N combined with soil inorganic N concentrations and net N transformation rates could be used to identify primary N transformation processes. More frequent samplings would be needed to differentiate burning impacts from the seasonal impacts on soil N cycling processes. [ABSTRACT FROM AUTHOR]

Purpose: Prescribed burning is a forest management practice which can lead to nitrogen (N)-limited conditions. This study aimed to explore whether biological N2 fixation (BNF) remained the main source of N acquisition for two understorey Acacia species in a Eucalyptus-dominated suburban forest of subtropical Australia, 3 to 6 years after prescribed burning. Root-nodule bacteria associated with these acacias were also characterised to unravel the differences in rhizobial communities between sites and species. Material and methods: Two sites, burned 3 and 6 years before sample collection, were selected within a dry subtropical forest of south-east Queensland, Australia. Leaves were collected from individuals of Acacia disparrima and A. leiocalyx at each site to determine leaf total carbon (C) and N content, C and N isotope composition (δ13C and δ15N) and the percentage of N derived from atmospheric N2. Nodules were harvested from both acacia species at each site to isolate root nodule bacteria. Bacterial isolates were processed for 16S rDNA gene sequencing. Results and discussion: Generally, no differences were found in plant physiological variables between the two acacia species. Six years after the fire, both species still depended upon BNF for their N supply, with a higher dependence in winter than in summer. Fire, although of low intensity, was likely to have created a N-limited environment which induced the reliance of legumes on BNF. Root nodule bacteria were dominated by non-rhizobial endophytes, mainly from the Firmicutes phylum. No difference in nodule bacterial diversity was found between sites. The relative abundance of rhizobial genera varied amongst plant species and sites, with a shift in dominance from Bradyrhizobium to Rhizobium species between sites 1 and 2. Conclusions: Our results show that even 6 years after burning, ecosystem remained under N stress and BNF was still the main mechanism for N acquisition by the understorey legumes. [ABSTRACT FROM AUTHOR]

Mixed species plantings of teak (Tectona grandis) and flueggea (Flueggea flexuosa) were introduced as a method for overcoming the reluctance of local growers to thin their teak. Flueggea is a well-used local species and removal of the flueggea for personal use would effectively thin the entire stand over time. Stocking rates and tree species composition are two important factors affecting tree growth and yield when a mixed species plantation is established. This study aimed to investigate the effects of stocking rates on early teak growth in a mixed species system in a humid tropical region of Western Province, Solomon Islands. The experimental design included: teak planted as a monoculture at standard stocking of 833 stems per hectare (sph) (Treatment 1); teak planted in rows alternating with 2 rows of flueggea at 833 sph; 625 sph; and 416 sph (Treatments 2,3 and 4 respectively); and teak planted in alternating rows with a single row of flueggea at 833 sph (Treatment 5). Teak basal area was optimum at the lowest stocking rates of 412 and 625 sph for both species. However, teak yield (volume per hectare) was greater in the higher stocking rate treatments. Teak basal area mean annual increment (BA MAI) decreased in higher stocking rates between the age of 4 and 5 years indicating the onset of suppression and the need for progressive thinning. Under correct silvicultural maintenance, the 833 sph planting density offers the benefits of higher stocking and lower maintenance. As the present investigation was confined to the establishment phase for teak, more studies are needed to understand the system development to maturity. [ABSTRACT FROM AUTHOR]

Purpose: High demand for teak (Tectona grandis L.f.), a species of economic importance, was the reason Solomon Islands experienced a surge in community-wide planting of monoculture teak stands in the last two decades. Mixed species planting of teak and flueggea (Flueggea flexuosa Muell. Arg.) was introduced to overcome the reluctance of growers to thin their stands. However, there is lack of information on the effect of changing from monoculture to mixed species plantings on the cycling of nutrients especially carbon (C) and nitrogen (N). Materials and methods: This study assessed litter quantity and quality, total C (TC), total N (TN), C:N ratio and C and N isotope compositions (δ13C and δ15N) over 18 months at two sites (Ringgi and Poitete). The treatments included teak planted at 833 stems per hectare (sph) (T1), teak planted in rows with two rows of flueggea at 833 sph (T2), 625 sph (T3) and 416 sph (T4), and teak planted in alternating rows with flueggea at 833 sph (T5). Results and discussion: Treatment 1 (T1) produced significantly higher total litter than T4 at Ringgi. However, based on individual tree litterfall production, teak in T4 (lowest stocking rate) at both trials produced higher litter per tree than the teak in T3, T2, T5 and T1 while there was no significant difference with litter production of flueggea. An enrichment of litter δ15N was observed over time in either species, which suggested an increased N loss and transformations in both experimental sites. When comparing each treatment and using individual tree productivity, T4 significantly produced and returned higher litter TC and TN than T3, T2, T5 and T1. Conclusions: Overall, individual tree productivity demonstrated that mixed species stands had a significant potential for cycling higher rates of C and N than monoculture teak stands. Therefore, establishment of mixed species stands, especially T4 and T3, was recommended as a practical measure to address the widely experienced problem of reluctance by growers to thin high value trees while preserving the balance of C and N inputs into the ground. [ABSTRACT FROM AUTHOR]

Aims: Corymbia spp. (previously included in the genus Eucalyptus) are common species in sub/tropical Australia and produce high quality timber and round logs. Thinning of native forests helps to preserve native tree species and is more sustainable than replacing native forest stands with mono-species plantations to produce timber. This study aimed to explore the effects of native forest thinning on soil-plant carbon (C) and nitrogen (N) dynamics in two experimental sites, Esk (5 years post-thinning) and Herberton (7 years post-thinning), situated in Queensland, Australia. Methods: The two sites had different thinning regimes. The final stocking rates varied between 75 and 200 stems ha at Esk and between 250 and 400 stems ha at Herberton. The thinned plots were compared to un-thinned plots. Soil samples were collected to measure labile C and N. Leaf samples were collected from C. variegata and C. citriodora in Esk and Herberton respectively. Results: Thinning did not change soil total C, total N, δN and inorganic N at either Esk or Herberton. However, at Esk, intensive thinning resulted in decreases in water soluble total N (WSTN). Foliar δC did not vary with respect to thinning whereas foliar δN values were more enriched in thinned areas than those of un-thinned plots. The stepwise linear regression indicated that both foliar total N and δN were explained mainly by soil TN and WSTN. Conclusions: Thinning did not change soil C and N most likely due to the retention of thinned materials on site and their incorporation into soil. Foliar δC was not thinning-dependent due to homeostatic maintenance of the ratio of intercellular to ambient CO concentrations during photosynthesis. In our study, soil N was not a limiting factor for foliar N, however, foliar N was mainly driven by WSTN which may foreshadow a possible N limitation in severely thinned plots in the long term. We conclude that forest thinning does not decrease soil C and N availability in native Corymbia forests for several years post-thinning if the thinned materials are retained on site. [ABSTRACT FROM AUTHOR]

Tree mono-plantations are susceptible to soil nutrient impoverishment and mixed species plantations have been proposed as a way of maintaining soil fertility while enhancing biodiversity. In the Solomon Islands, mixed species plantations where teak (Tectona grandis) is inter-planted with a local tree species (Flueggea flexuosa) have been used as an alternative to teak mono-plantations and are expected to increase soil microbial diversity and modify microbial biogeochemical processes. In this study, we quantified the abundance of microbial functional genes involved in the nitrogen (N) cycle from soil samples collected in teak, flueggea, and mixed species plantations. Furthermore, we measured soil properties such as pH, total carbon (C) and total N, stable N isotope composition (δ15N), and inorganic N pools. Soil pH and δ15N were higher under teak than under flueggea, which indicates that intercropping teak with flueggea may decrease bacterial activities and potential N losses. Higher C:N ratios were found under mixed species plantations than those under teak, suggesting an enhancement of N immobilization that would help preventing fast N losses. However, inorganic N pools remained unaffected by plant cover. Inter-planting teak with flueggea in mixed species plantations generally increased the relative abundance of denitrification genes and promoted the enrichment of nosZ-harboring denitrifiers. However, it reduced the abundance of bacterial amoA (ammonia monooxygenase) genes compared to teak mono-plantations. The abundance of most denitrification genes correlated with soil total N and C:N ratio, while bacterial and archeal nitrification genes correlated positively with soil NH4+ concentrations. Altogether, these results show that the abundance of bacterial N-cycling functional guilds vary under teak and under mixed species plantations, and that inter-planting teak with flueggea may potentially alleviate N losses associated with nitrification and denitrification and favor N retention. Mixed plantations could also allow an increase in soil C and N stocks without losing the source of income that teak trees represent for local communities. [ABSTRACT FROM AUTHOR]

Purpose: Rising levels of nitrogen (N) deposition are influencing urban forest carbon (C) and N dynamics due to greater human disturbance compared to those in rural areas. N deposition in combination with increased atmospheric carbon dioxide (CO) and water limitation may alter C and N storage in urban forests. This review aimed to provide a better understanding of N and C storage under N deposition scenarios in urban forests. Results and discussion: Globally, fuel combustion and biomass burning contribute in approximately 70 and 16 % of the NO emission respectively. It is also estimated that NH and NO are two to four times higher in urban forests compared to rural areas. However, higher N deposition may not always result in increased N and C storage in urban forests. In fact, urban forests may even show early symptoms of N and C losses under climate change. For example, urban forests in fire-prone areas require higher frequency of burning to reduce the threat of wildfires, leading to an acceleration of C and N loss. Additionally, chronic N deposition may result in an early N loss in urban forests due to faster N saturation and soil acidification in urban forests compared to rural forests. Studies of N deposition on urban forests using N isotope composition (δN) also showed that N loss from urban forests can occur through the direct leaching of the deposited NO-N. We also noted that using different N signal of soil and plant in combination of tree ring δN may provide a better understanding of N movement in urban forests. Conclusions: Although urban forests may become a source of C and N faster than rural forests, N-limited urban forests may benefit from N deposition to retain both N and C stocks longer than non-N-limited urban forests. Appropriate management practices may also help to delay such symptoms; however, the main source of emission still needs to be managed to reduce both N deposition and rising atmospheric CO in urban forests. Otherwise, the N and C stocks in urban forests may further decline when prolonged drought conditions under global climate change increase the frequency of fires and reduce plant photosynthesis. [ABSTRACT FROM AUTHOR]

Eucalyptus spp. is a dominant tree genus in Australia and most Eucalyptus spp. are canopy dominant species. In Australian natural forests, Eucalyptus spp. commonly are associated with understorey legumes which play a crucial role for ecological restoration owing to their nitrogen (N) fixing ability for replenishing the soil N lost after frequent prescribed burning. This study aimed to explore to what extent physiological responses of these species differ 7 and 12 years after last fire. Two most common understorey Acacia spp., Acacia leiocalyx and A. disparrima, as well as one non-leguminous Eucalyptus resinifera, were studied due to their dominance in the forest. Both A. leiocalyx and A. disparrima showed higher carbon (C) assimilation capacity, maximum photosynthetic capacity, and moderate foliar C/N ratio compared with E. resinifera. A. leiocalyx showed various advantages compared to A. disparrima such as higher photosynthetic capacity, adaptation to wider light range and higher foliar total N (TN. A. leiocalyx also relied on N-fixing ability for longer time compared to A. disparrima. The results suggested that the two Acacia spp. were more beneficial to C and N cycles for the post burning ecosystem than the non-N-fixing species E. resinifera. A. leiocalyx had greater contribution to complementing soil N cycle long after burning compared to A. disparrima. [ABSTRACT FROM AUTHOR]

Purpose: This study aimed to evaluate the effects of tree cover (tree plots ( Acacia disparrima and Eucalyptus crebra) vs. non-tree plots) on soil labile carbon (C) and nitrogen (N) recovery in revegetation trials, without and with topsoil removal, 3 years following tree planting. Materials and methods: Soil total C (TC) and total N (TN), hot-water-extractable organic C (HWEOC), hot-water-extractable total N (HWETN), microbial biomass (MB) and potentially mineralisable N (PMN) were measured. Results and discussion: Where topsoil had not been removed, soil TN, HWEOC, HWETN and PMN were significantly higher in the tree-covered plots compared to non-tree-covered plots. In contrast, tree cover did not significantly increase soil labile C and N when topsoil had been removed. Both leguminous and non-leguminous species ( A. disparrima and E. crebra) had similar effects on soil labile C and N. Tree cover did not accelerate C and N recovery at their early stage of establishment when topsoil had been removed. Therefore, our finding suggests that topsoil-removed plots may need more than 3 years to replenish soil C and N to their initial levels. There was also a clear indication of C and N depletion in the topsoil in areas not covered by trees even though the topsoil had not been removed. Conclusions: Altogether, these results demonstrate the importance of longer-term monitoring of revegetation areas to be able to assess its success in improving soil quality. [ABSTRACT FROM AUTHOR]

This study aimed to evaluate the improvement in soil fertility and plant nutrient use in a macadamia orchard following biochar application. The main objectives of this study were to assess the effects of poultry litter and green waste biochar applications on nitrogen (N) cycling using N isotope composition (δN) and nutrient availability in a soil-plant system at a macadamia orchard, 5 years following application. Biochar was applied at 10 t ha dry weight but concentrated within a 3-m diameter zone when trees were planted in 2007. Soil and leaf samples were collected in 2012, and both soil and foliar N isotope composition (δN) and nutrient concentrations were assessed. Both soil and foliar δN increased significantly in the poultry litter biochar plots compared to the green waste biochar and control plots. A significant relationship was observed between soil and plant δN. There was no influence of either biochars on foliar total N concentrations or soil NH-N and NO-N, which suggested that biochar application did not pose any restriction for plant N uptake. Plant bioavailable phosphorus (P) was significantly higher in the poultry litter biochar treatment compared to the green waste biochar treatment and control. We hypothesised that the bioavailability of N and P content of poultry litter biochar may play an important role in increasing soil and plant δN and P concentrations. Biochar application affected soil-plant N cycling and there is potential to use soil and plant δN to investigate N cycling in a soil-biochar-tree crop system. The poultry litter biochar significantly increased soil fertility compared to the green waste biochar at 5 years following biochar application which makes the poultry litter a better feedstock to produce biochar compared to green waste for the tree crops. [ABSTRACT FROM AUTHOR]

Purpose: To successfully establish revegetation, there is a need for weed control. Herbicide application and top soil removal (scalping) may be used to suppress weeds. However, scalping alters soil water and nitrogen availability which in turn may affect plant physiology and performance during the early phase of establishment. Materials and methods: A field trial was established in south east Queensland, Australia, to examine weed control methods, including herbicide application and scalping. Plant survival, mean periodic height gain, specific leaf area and leaf-level physiological traits were measured for Acacia concurrens Pedley and Eucalyptus crebra F. Muell. for 17 months following tree establishment. Results and discussion: Plant survival and growth of A. concurrens were superior in the scalped area compared to the herbicide area, whereas neither survival nor growth of E. crebra was influenced by weed control methods. In general, there were no or little effect of site preparation practices on carbon and nitrogen isotope composition, specific leaf area, photosynthesis, maximum photosynthesis and instantaneous water-use efficiency. Photosynthetic capacity was not influenced by site preparation practices as reflected through the maximum rate of carboxylation and maximum rate of electron transport. Conclusions: Despite altering soil nutrient availability in the scalped areas and high weed coverage in the herbicide areas, there was no substantial alteration in plant physiology for both species. E. crebra was less affected by either low nutrient availability in the scalped areas or high weed coverage in the herbicide areas compared to A. concurrens. Therefore, E. crebra could be considered as a valuable species to revegetate degraded lands. [ABSTRACT FROM AUTHOR]

Purpose: This study investigated how nitrogen (N) nutrition and key physiological processes varied under changed water and nitrogen competition resulting from different weed control and fertilisation treatments in a 2-year-old F hybrid ( Pinus elliottii Engelm var. elliottii × P. caribaea var. hondurensis Barr. ex Golf.) plantation on a grey podzolic soil type, in Southeast Queensland. Materials and methods: The study integrated a range of measures including growth variables (diameter at ground level (DGL), diameter at breast height (DBH) and height (H)), foliar variables (including foliar N concentration, foliar δC and δN) and physiological variables (including photosynthesis (A), stomatal conductance (g), transpiration ( E), intrinsic water use efficiency (WUE) ( A/g) and xylem pressure potential (Ψ)) to better understand the mechanisms influencing growth under different weed control and fertilisation treatments. Five levels of weed control were applied: standard (routine), luxury, intermediate, mechanical and nil weed control, all with routine fertilisation plus an additional treatment, routine weed control and luxury fertilisation. Relative weed cover was assessed at 0.8, 1.1 and 1.6 years after plantation establishment to monitor the effectiveness of weed control treatments. Soil investigation included soil ammonium (NH-N), nitrate (NO-N), potentially mineralizable N (PMN), gravimetric soil moisture content (MC), hot water extractable organic carbon (HWETC), hot water extractable total N (HWETN), total C, total N, stable C isotope composition (δC), stable N isotope composition (δN), total P and extractable K. Results and discussion: There were significant relationships between foliar N concentrations and relative weed cover and between tree growth and foliar N concentration or foliar δN, but initial site preparation practices also increased soil N transformations in the planting rows reducing the observable effects of weed control on foliar δN. A positive relationship between foliar N concentration and foliar δC or photosynthesis indicated that increased N availability to trees positively influenced non-stomatal limitations to photosynthesis. However, trees with increased foliar N concentrations and photosynthesis were negatively related to xylem pressure potential in the afternoons which enhanced stomatal limitations to photosynthesis and WUE. Conclusions: Luxury and intermediate weed control and luxury fertilisation positively influenced growth at early establishment by reducing the competition for water and N resources. This influenced fundamental key physiological processes such as the relationships between foliar N concentration, A, E, g and Ψ. Results also confirmed that time from cultivation is an important factor influencing the effectiveness of using foliar δN as an indicator of soil N transformations. [ABSTRACT FROM AUTHOR]

During revegetation, the maintenance of soil carbon (C) pools and nitrogen (N) availability is considered essential for soil fertility and this study aimed to evaluate contrasting methods of site preparation (herbicide and scalping) with respect to the effects on soil organic matter (SOM) during the critical early establishment phase. Soil total C (TC), total N (TN), hot-water extractable organic C (HWEOC), hot-water extractable total N (HWETN), microbial biomass C and N (MBC and MBN), total inorganic N (TIN) and potentially mineralizable N (PMN) were measured over 53 weeks. MBC and MBN were the only variables affected by herbicide application. Scalping caused an immediate reduction in all variables, and the values remained low without any sign of recovery for the period of the study. The impact of scalping on HWETN and TIN lasted 22 weeks and stabilised afterwards. MBC and MBN were affected by both herbicide and scalping after initial treatment application and remained lower than control during the period of the study but did not decrease over time. While scalping had an inevitable impact on all soil properties that were measured, that impact did not worsen over time, and actually improved plant growth (unpublished data) while reducing site establishment costs. Therefore, it provides a useful alternative for weed control in revegetation projects where it is applied only once at site establishment and where SOM would be expected to recover as canopy closure is obtained and nutrient cycling through litterfall commences. [ABSTRACT FROM AUTHOR]

Background and aim: Significant differences in tree growth were observed in an exotic pine plantation under different harvest residue management regimes at ages 2-10 years. However, the variations in tree growth between residue management treatments could not be explained by soil and foliar nutrient analyses, except by potassium (K) concentration. Therefore, this study determined the carbon isotope composition (δC) and oxygen isotope composition (δO) of current and archived foliar samples from the exotic pine plantation to establish relationships with foliar K concentration and tree growth indices as a means to determine changes in stomatal conductance (g) and photosynthetic rate (A) or water use efficiency (WUE), and therefore understand the variations in tree growth across treatments. Methods: The harvest residue treatments were: (1) residue removal, RR; (2) single level residue retention, RR; and (3) double level residue retention, RR. Foliar δC and δO were determined for samples at ages 2, 4, 6 and 10 years, and the atmospheric C discrimination (ΔC), intercellular CO concentration (C) and WUE were determined from the δC data. Litter needle δC and δO were also determined over 15 months between ages 9 and 10 years. These parameters or variables where correlated to each other as well as to the periodic mean annual increment of basal area (PAIB) and the periodic mean annual increment of tree diameter at breast height (PAID) across the treatments and over time. Foliar δC and δO were also related to published data of foliar K concentrations of the same trees. Results: Significant variations of foliar δC, and therefore WUE and ΔC, across treatments were only observed at ages 4 and 10 years old, and foliar δO at age 4 years old only. The results showed increasing foliar δC, δO and WUE, and decreasing ΔC and C i, from RR to RR treatments. However, while the WUE was positively related to the PAID and PAIB at age 4 years, it was negatively related to PAID and PAIB at age 10 years old. Litter needle δC, indicative of WUE, was also negatively related to the PAID at age 10 years old. . At age 4 years, foliar δC and δO were positively related with a steep slope of 7.70 ‰ across treatments, and that both isotopes were positively related to foliar K concentrations. Similarly, δO was negatively related to the ΔC. No significant relationship can be determined between foliar δC, or ΔC, and δO at age 10 years old. In addition, WUE was increasing ( p < 0.001) and ΔC and C decreasing ( p < 0.001) with decreasing PAID over time. Conclusions: The variations at age 4 years in foliar δC or ΔC and δO and increasing WUE with increasing growth rate suggest growth induced water-stress with increasing residue-loading rate as a result of the nutritional effect of the harvest residues on tree growth. At age 10 years, the negative relationships between WUE and PAID indicate nutrient limitation has an over-riding effect on δC variations rather than g. This was due to the lack of a significant relationship between foliar ΔC and δO at this age, as well as over time. [ABSTRACT FROM AUTHOR]

Three mulch treatments were tested for their ability to control erosion on a sloping site. Additionally, the choice of mulch can also enhance revegetation success and improve soil organic matter input. This study aimed to investigate the effects of three mulching treatments, hydro-seeding, granite mulch and forest mulch, on soil C and N pools at different positions on highly erodible slope with approximately 30 % gradient. Soil moisture, total C (TC), total N (TN), hot water-extractable organic C (HWEOC), hot water-extractable total N (HWETN), microbial biomass C and N (MBC and MBN), inorganic N and potentially mineralisable N were measured. All variables were significantly higher in soils amended with forest mulch than those with hydro-seeding and granite mulch, for the same slope positions. Soil moisture was significantly higher in the lower slope position than middle and upper slope positions in hydro-seeding and granite mulch treatments, whereas no slope effect was observed on soil moisture under the forest mulch application. In the forest mulch treatment, the upper slope position had higher soil TC, TN, HWEOC, HWETN, MBC, MBN, NO-N and total inorganic N than the middle and lower slope positions. Five years following mulch application, forest mulch still exerted a significant influence on soil fertility compared to the other treatments and the influence on soil moisture suggests that this treatment would be the most effective in the control of water-driven soil erosion on this steep site. [ABSTRACT FROM AUTHOR]

Purpose: We investigated the effects of weed control and fertilization at early establishment on foliar stable carbon (δC) and nitrogen (N) isotope (δN) compositions, foliar N concentration, tree growth and biomass, relative weed cover and other physiological traits in a 2-year old F hybrid ( Pinus elliottii var. elliottii (Engelm) × Pinus caribaea var. hondurensis (Barr. ex Golf.)) plantation grown on a yellow earth in southeast Queensland of subtropical Australia. Materials and methods: Treatments included routine weed control, luxury weed control, intermediate weed control, mechanical weed control, nil weed control, and routine and luxury fertilization in a randomised complete block design. Initial soil nutrition and soil fertility parameters included (hot water extractable organic carbon (C) and total nitrogen (N), total C and N, C/N ratio, labile N pools (nitrate (NO) and ammonium (NH)), extractable potassium (K)), soil δN and δC. Relative weed cover, foliar N concentrations, tree growth rate and physiological parameters including photosynthesis, stomatal conductance, photosynthetic nitrogen use efficiency, foliar δN and foliar δC were also measured at early establishment. Results and discussion: Foliar N concentration at 1.25 years was significantly different amongst the weed control treatments and was negatively correlated to the relative weed cover at 1.1 years. Foliar N concentration was also positively correlated to foliar δN and foliar δC, tree height, height growth rates and tree biomass. Foliar δN was negatively correlated to the relative weed cover at 0.8 and 1.1 years. The physiological measurements indicated that luxury fertilization and increasing weed competition on these soils decreased leaf xylem pressure potential (Ψ) when compared to the other treatments. Conclusions: These results indicate how increasing N resources and weed competition have implications for tree N and water use at establishment in F hybrid plantations of southeast Queensland, Australia. These results suggest the desirability of weed control, in the inter-planting row, in the first year to maximise site N and water resources available for seedling growth. It also showed the need to avoid over-fertilisation, which interfered with the balance between available N and water on these soils. [ABSTRACT FROM AUTHOR]

Purpose: This study evaluated the potential of using hot water extractable phosphorus (P) pools as a method to assess the impacts of harvest residue management on the bioavailability of P in an exotic pine plantation of southeast Queensland, Australia. Materials and methods: This study was carried out under three harvest residue management regimes: (1) residue removal, RR; (2) single-level residue retention (operational level), RR; and (3) double level of residue retention, RR, established immediately following clear-cut harvesting in a randomised complete block experiment. Soil was sampled after 24 months of the residue management regimes applied and analysed for hot water extractable inorganic P (HWEIP), hot water extractable organic P (HWEOP) and total P (HWETP), in relation to hot water extractable organic C (HWEOC) and N (HWEON), calcium chloride extractable P (CaCl_P), bicarbonate extractable P (NaHCO_P) and fluoride extractable P (Bray1_P). Results and discussion: The HWEIP and CaCl_P concentrations showed no significant variations amongst the treatments, while Bray1_P, NaHCO_P and the HWEOP P pools were only significantly greater in the RR treatment than the RR treatment. In contrast, the HWETP pool showed highly significant ( p < 0.005) differences amongst all the treatments. In addition, both the HWEOP and HWETP were significantly related to the HWEOC and the total C, in contrast to the lack of such relationships with soil total P, suggesting their association with the HWEOC released through residue decomposition. Conclusions: This study showed that HWETP is a more sensitive measure of labile soil P and has the potential to be used as an indicator of management practices, particularly in cases where high spatial variations in soil P concentrations might confound P responses. [ABSTRACT FROM AUTHOR]

Purpose: Understorey Acacia spp. plays an important role in post-fire restoration because these understorey plants are tolerant to stress conditions. We investigated how the ecophysiological status of two species of understorey, Acacia leiocalyx and Acacia disparrima, varied depending on the plant growth stage after prescribed burning. Materials and methods: Plants were grouped in different size classes, namely seedlings, small and medium sizes, and physiological variables such as foliar gas exchange, water use efficiency and light dependency were measured at two experimental sites subjected to prescribed burning. Results and discussion: A. leiocalyx showed higher symbiotic N fixation and photosynthetic capacity compared to A. disparrima regardless of plant-size classes at both experimental sites. This could explain the greater relative growth rate of A. leiocalyx than that of A. disparrima. However, A. disparrima is more tolerant to shady conditions than A. leiocalyx. Conclusions: This finding may be an indication of how well these two species recover after fire, although A. leiocalyx may have faster regrowth, as it is fixing more N. [ABSTRACT FROM AUTHOR]

Background and aims: The aim of weed control and fertilization in forest plantations was to increase tree growth by reducing competition for available nutrients and water. However, treatments that influence weed biomass can also have significant impacts on soil carbon (C) and nitrogen (N) cycling which can in turn lead to changes in the dynamics of stable C (δC) and N (δN) isotope compositions in soils and tree foliage. Methods: We examined the key C and N cycling processes influenced by routine and luxury weed control and fertilization treatments as reflected by soil and foliar δC and δN and long-term tree growth in an 8-year old F hybrid pine ( Pinus elliottii x P. caribaea) plantation in southeast Queensland, Australia. Weed control treatments varied by treatment frequency and intensity while fertilization treatments varied by the application of N, phosphorus (P), potassium (K) and micronutrients. Different soil and canopy sampling positions were assessed to determine if sampling position enhanced the relationships among soil N transformations and tree N use, water use efficiency and carbon gain under the early establishment silviculture. Results: Routine weed control was associated with increased weed biomass returned to the soil, compared with luxury weed control. Soil δC increased at the 0-5 cm soil sampling depth in both the inter-planting (IPR) and planting row (PR) as a result of the routine weed control treatments. In addition, soil δC was significantly higher as a result of fertilisation treatment in the 0-5 cm soil sampling depth in the PR. Soil δC was negatively correlated to soil δN at the 0-5 cm soil sampling depth in the IPR. Soil δN increased in the 0-5 and 5-10 cm soil sampling depths in the IPR, as a result of more frequent (luxury) weed control. Foliar δN and tree water use efficiency (WUE) (as indicated by foliar δC) were positively correlated with tree growth at age 8 years. While relationships between δC and δN in the soil and foliage varied depending on soil sampling depth and position, and with canopy sampling position where there were consistent relationships between soil δC (or δN) and foliar δN. Conclusions: This study demonstrates how early establishment silviculture has important implications for soil C and N cycling and how soil δC and δN were consistent with changes in soil C cycling and N transformations as a result of weed control treatments, while foliar δN was linked to more rapid N cycling as reflected in the soil δN, which increased tree growth and tree WUE (as reflected by foliar δC). [ABSTRACT FROM AUTHOR]

Purpose: Residue retention is important for nutrient and water economy in subtropical plantation forests. We examined decomposing hoop pine ( Araucaria cunninghamii Ait. Ex D. Don) residues-foliage, branches, and stem wood-to determine the changes in structural chemistry that occur during decomposition. Materials and methods: Residues were incubated in situ using 0.05 m microplots. We used solid-state C nuclear magnetic resonance (NMR) spectroscopy to determine the structural composition of harvest residues in the first 24 months of decomposition. Results and discussion: The spectral data for branch and stem residues were generally similar to one another and showed few changes during decomposition. The lignin content of branch and foliage residues decreased during decomposition. When residues were mixed together during decomposition, the O-alkyl fraction of foliage decreased initially then increased up to 24 months, while the alkyl carbon (C) fraction exhibited the opposite pattern. The decomposition of woody hoop pine residues (branch and stem wood) is surprisingly uniform across the major C forms elucidated with C NMR, with little evidence of preferential decomposition. When mixed with branch and stem materials, foliage residues showed significant short- and long-term compositional changes. This synergistic effect may be due to the C/N ratio of the treatments and the structure of the microbial decomposer community. Conclusions: Twenty-four months of decomposition of hoop pine residues did not result in substantial accumulation of recalcitrant C forms, suggesting that they may not contribute to long-term C sequestration. [ABSTRACT FROM AUTHOR]

Purpose: It is anticipated that global climate change will increase the frequency of wildfires in native forests of eastern Australia. Understorey legumes such as Acacia species play an important role in maintaining ecosystem nitrogen (N) balance through biological N fixation (BNF). This is particularly important in Australian native forests with soils of low nutrient status and frequent disturbance of the nutrient cycles by fires. This study aimed to examine N enrichment and N natural abundance techniques in terms of their utilisation for evaluation of N fixation of understorey acacias and determine the relationship between species ecophysiological traits and N fixation. Materials and methods: A trial was established at sites 1 and 2 located at Toohey Forest, Queensland, Australia, a eucalypt-dominated native forest, to examine the determination of BNF using N enrichment and N natural abundance methods. Toohey Forest is an urban forest and subjected to frequent fuel reduction burns to protect the adjacent properties. Plant physiological status was measured to determine the relationship between physiological and N fixation activities. Results and discussion: Both N enrichment and N natural abundance techniques may be used to estimate N fixation of acacia tree species. The estimation of BNF using N enrichment was higher than those of the N natural abundance method. A grass reference plant, Themeda triandra, as well as tree reference plants provided an appropriate δN signal. Potential B values for Acacia spp. between −0.3‰ and 1.0‰ provided an acceptable BNF estimation. This suburban forest is located nearby a busy highway leading to N deposition over time with consequent negative δN signal. This N deposition may explain the separation between the δN signal of the acacias and that of the reference plants which led to the successful use of the N natural abundance technique. Acacia leiocalyx demonstrated greater N fixation as well as photosynthesis and instantaneous water use efficiency than Acacia disparimma. However, no strong relationship between plant photosynthesis and N fixation was observed in this study. A high within-treatment variation may have masked the relationships between plant BNF activities and photosynthesis Conclusions: The N natural abundance technique is preferred to be used for future studies as it is simple and inexpensive compared with N enrichment method. The dependence of both species on BNF at site 2, where fuel reduction burning had not taken place for 8 years, suggests that the frequent burning impoverished the soil, and this has wider implications as higher fire frequencies are to be expected in other Australian ecosystems as a result of global climate change. [ABSTRACT FROM AUTHOR]

Purpose: There is considerable interest in finding a cost-effective method of site preparation that effectively controls weeds during planting and further reduces the need for recurring herbicide applications. In this study, two weed control methods, herbicide and scalping, were examined. Both methods may have implications for soil organic matter (SOM) dynamics and nitrogen (N) which could consequently affect plant survival and vegetation establishment. This study aimed to investigate the dynamics of SOM, carbon (C) and N pools under site manipulation practices and the associated early plant survival and growth in tropical Australia. Materials and methods: A field trial was established in Central Queensland to examine the recovery of SOM, C and N pools following scalping and the alternative site preparation technique of sequential herbicide application. Both were contrasted with control plots which received neither treatment. Plant survival and growth were also monitored to improve our understanding of plant response to site preparation practices. Results and discussion: Scalped plots showed significantly lower values for labile C and N pools compared with the herbicide treatment and control. Generally, there was no significant difference between the herbicide and control for any of the parameters tested. Our observation indicated that herbicide application was significantly less effective than scalping to control weeds. A general decline in SOM parameters was observed in all the plots, including the control during the trial. Drought conditions were considered to be a major factor in the overall decline of SOM. Despite removal of the top soil, there was no significant difference in plant survival between herbicide and scalped areas (81% and 79% survival, respectively). Plant growth was not affected by the treatments in the first 6 months when weed competition in the herbicide areas and low nutrient availability in the scalped plots would have been significant factors in controlling growth rates. However, plants in the herbicide areas, irrespective of species, showed stronger growth than those in the scalped plots at week 61 when they had outgrown the weed competition. It is likely that differences in plant growth response to treatments will become negligible over time. Conclusions: Top soil removal was more effective than the use of herbicide in the long-term control of weeds. However, lower SOM and N availability in the scalped areas did not affect plant survival rates when compared with that of the herbicide areas. Whilst the preservation of soil organic matter is considered to be vital in short-term cropping systems, our results indicate that this is not the case for woody vegetation establishment and, in terms of cost and reduction of chemical use, removal of the organically rich top soil, with its accompanying seed burden may be both practical and desirable. [ABSTRACT FROM AUTHOR]

Introduction: The objective of this review was to provide a better understanding of how global climate change and fire influence the occurrence of understorey legumes and thereby biological nitrogen (N) fixation rates in forest ecosystems. Legumes are interesting models since they represent an interface between the soil, plant, and microbial compartments, and are directly linked to nutrient cycles through their ability to fix N. As such, they are likely to be affected by environmental changes. Result and discussion: Biological N fixation has been shown to increase under enriched CO conditions, but is constrained by the availability of phosphorus and water. Climate change can also influence the species composition of legumes and their symbionts through warming, altered rainfall patterns, or changes in soil physicochemistry, which could modify the effectiveness of the symbiosis. Additionally, global climate change may increase the occurrence and intensity of forest wildfires thereby further influencing the distribution of legumes. The establishment of leguminous species is generally favored by fire, as is N fixation. This fixed N could therefore replenish the N lost through volatilization during the fire. However, fire may also generate shifts in the associated microbial community which could affect the outcome of the symbiosis. Conclusion: Understorey legumes are important functional species, and even when they cannot reasonably be expected to reestablish the nutrient balance in forest soils, they may be used as indicators to monitor nutrient fluxes and the response of forest ecosystems to changing environmental conditions. This would be helpful to accurately model ecosystem N budgets, and since N is often a limiting factor to plant growth and a major constraint on C storage in ecosystems, would allow us to assess more precisely the potential of these forests for C sequestration. [ABSTRACT FROM AUTHOR]

Soil carbon (C) and nutrient pools under different plantation weed control and fertilizer management treatments were assessed in a 7-year-old, F1 hybrid ( Pinus elliottii var. elliottii × Pinus caribaea var. hondurensis) plantation in southeast Queensland, Australia. This research aimed to investigate how early establishment silvicultural treatments would affect weed biomass, soil C, nitrogen (N) and other nutrient pools; and soil C (δ13C) and N isotope composition (δ15N) to help explain the key soil processes regulating the soil C and nutrient pools and dynamics. Soils were sampled in June 2006 in both the planting row and in the inter-planting row at three depths (0–5, 5–10, and 10–20 cm). Soil parameters including total and labile C and N pools; soil δ13C and δ15N; total phosphorus (P); extractable potassium (K); moisture content and weed biomass were investigated. The luxury weed control treatments significantly reduced weed biomass and its organic residues returned to the soil in the first 7 years of plantation development. This resulted in significant variations at some depths and positions in soil δ13C, δ15N, extractable K, hot water extractable organic C (HWEOC), hot water extractable total N (HWETN), potentially mineralizable N (PMN), and soil moisture content (MC). Luxury weed control in the absence of luxury fertilization also significantly decreased extractable K. There was a significant interaction between soil depth and sampling position for soil total C, total N, HWEOC, and HWETN. Weed biomass correlated positively with soil total N, δ13C, PMN, MC, HWEOC, and HWETN. Luxury weed control treatments significantly reduced weed biomass leading to a reduction of soil organic matter. Soil δ13C and δ15, together with the other soil labile C and N pools, were sensitive and useful indicators of soil C dynamics and N cycling processes in the exotic pine plantation of subtropical Australia. [ABSTRACT FROM AUTHOR]

Purpose Hoop pine (Araucaria cunninghamii) is a nitrogen (N)-demanding native Australian softwood plantation species. Litter quality and its effects on soil mineral N and 15N transformations have not been well studied in the hoop pine plantation and adjacent native forest. The present study was conducted to determine the impact of 15N injection depth and litter additions on the dynamics and fate of mineral 15N and also to compare the difference in litter quality, 15N dynamics, and fate between the hoop pine plantation (HP) and the adjacent native forest (NF). Materials and methods The experiments were done in the Yarraman State Forest (26°52′ S, 151°51′ E), southeastern Queensland. Materials of litter addition were prepared on the basis of ten random samples of litters taken from the NF and HP sites using a 1x1-m quadrat. Litter additions were defined as: SL represented the average condition of forest floor in the forest ecosystems and DL represented the double average amount of litters in the forest ecosystem. Experiment 1 covered 2 forest types (NF and HP)x3 litter rates (nil litter, SL, and DL)x3 15N injection depths (0, 2.5, and 5.0 cm). Experiment 2 included 2 forest types (NF and HP)x2 litter rates (nil litter and SL)x3 injection depths (0, 2.5, and 5.0 cm) of distilled water. The in situ core incubation method was used with an incubation period of 28 days. The isotope ratio of mineral N or/and total N (soil and litter) were analyzed using an isotope ratio mass spectrometer with a Eurovector elemental analyzer (Isoprime-EuroEA 3000). Results Total N and δ15N were significantly higher, and C/N ratios and δ13C were significantly lower in the NF litters than in the HP litters. The NF litters had significantly lower total 15N and total 15N recovery than the HP litters after 15N addition. Litter addition had no significant effect on mineral 15N transformations and δ15N in the NF soil, but decreased 15NO3 --N, mineral 15N, and δ15N and increased immobilized 15N in the HP soil. The depth of added 15NH4 + significantly altered total 15N, δ15N, and total 15N recovery in the litters, whereas it did not influence 15NH4 +-N, 15NO3 --N, mineral 15N, or immobilized 15N in soils in the two forest ecosystems.… [ABSTRACT FROM AUTHOR]

Background, aim, and scope Mulching is frequently used to overcome the drought problem in hardwood plantations that are increasingly being established in lower rainfall areas of Queensland, Australia because of increasing land values. In addition to soil water content, soil nitrogen (N) availability is another critical determinant of plantation productivity in these areas. The purpose of this study was to understand how soil mineral N dynamics, in situ N mineralization, and the fate of fertilized N would be affected by mulching during the early establishment of hardwood plantations. Materials and methods Two treatments (mulching, 1.57-kg m[sup-2] site preparation residues, and nonmulching) were applied to six 24-m-wide by 67.2-m-long plots at Pechey (27° 18' S, 152° 3' E) in southeast Queensland, Australia. At each sampling, two in situ N mineralization tubes were driven into the ground to a depth of 10 cm. One tube was immediately removed to provide baseline data for that sampling cycle. Another tube was left in situ for 1 month after which it was removed and a further two tubes were inserted to repeat the cycle. Sampling took place over 12 consecutive cycles, spanning one calendar year, commencing in January 2005. Between January and March 2005, another pair of soil tubes was driven into the ground to examine the fate of [sup15]N-labeled fertilizer. Briefly, 20-mL [sup15]N-labeled (NH[sup4])[sup2]SO[sub4] (10.3 at % [sup15]N) solution, containing 1.58 mg N, was uniformly applied on the soil surface of the tubes, giving 2.75 kg/ha N in each soil tube. Then, one tube was removed immediately and another left for I month as described above. Mineral N in all soil tubes was extracted with 2 M KCI. KCI extracts were analyzed colorirnetrically for NH[sub4][sup+]-N and NO[sub3][sup-]-N using a Lachat Autoanalyzer. The isotope ratio of mineral N and total N in [sup15]N-labeled tubes was analyzed using an isotope ratio mass spectrometer with a Eurovector elemental analyzer (Isoprime-EuroEA 3000). Results and discussion Mulching had no significant effect on net soil N mineralization during the 12-month period but had a significantly negative effect on net nitrification when net soil N mineralization was partitioned into net nitrification and net ammonification. Net nitrification constituted more than 85% of net N mineralization for both treatments. Nitrification was significantly correlated with air maximum temperature but poorly correlated with soil moisture. The results of unlabeled and [sup15]N-Iabeled in situ N mineralization experiments showed that reduced nitrification and increased N immobilization resulting from mulching were the main reasons for the lower mineral N of mulched soil in the early establishment period of hardwood plantation in subtropical Australia. Conclusions, recommendations, and perspectives The field incubation results indicate that if soil is mulched with site preparation residues, net nitrification and hence mineral N are lower than nonmulched soil during the first 12-month establishment period of hardwood plantation in subtropical Australia. Increased soil nitrification in the nonmulching treatment means greater potential for N losses through leaching and denitrification. N immobilization as a result of mulching implied that more N was retained in the soil, which may benefit the trees in the longer term. However, long-term research may be necessary to substantiate the conclusion. [ABSTRACT FROM AUTHOR]

Foliar gas exchange and carbon (δ13C) and oxygen (δ18O) isotope ratios were measured in a young blackbutt (Eucalyptus pilularis Sm.) plantation subjected to four weed control treatments defined by the width of the weed-free strip maintained for the first 12 months after planting. Treatments were: 2-m-wide weed-free strip (50% of plot area, 2.0MWC), 1.5-m-wide weed-free strip (37.5% of plot area, 1.5MWC), 1-m-wide weed-free strip (25% of plot area, 1.0MWC) and no weed control (NWC). Our objectives were to determine (1) if decreasing the width of the weed control strip (decreasing herbicide use) affected growth and leaf photosynthesis of the plantation, and (2) the effects of the weed control regimes on variations in relative stomatal and biochemical limitations to photosynthesis. Trees in the 1.0MWC treatment had lower foliar light-saturated photosynthetic rate (Asat) than trees in the 2.0MWC treatment. An increase in metabolic limitation was responsible for the decrease in Asat in the 1.0MWC trees, which was also partly confirmed by the isotopic data. Compared with trees in the 1.0MWC, 1.5MWC and 2.0MWC treatments, Asat of NWC trees was significantly lower, a difference that was attributable mainly to stomatal limitation and to a lesser extent to biochemical limitation. The results support the conclusion that different weed control regimes cause differences in relative stomatal and biochemical limitations to plantation photosynthesis. This report contributes to a growing body of literature on competition for soil resources between trees and weeds. Our results highlight the usefulness of the stable isotopic method in supporting analysis of the response of net photosynthesis to varying intercellular CO2 concentration for determining the relative stomatal and non-stomatal limitations to photosynthesis under experimental conditions in the field. [ABSTRACT FROM AUTHOR]

Background, Aims and Scope. Harvest residues were formed into windrows to prevent nitrogen (N) losses through volatilisation and erosion that occurred following pile and burn operations in hoop pine (Araucaria cunninghamii Aiton ex A. Cunn.) plantations of subtropical Australia. We selected second rotation (2R) hoop pine sites where the windrows (10–15 m apart) had been formed 1, 2 and 3 years prior to sampling in order to examine soil carbon (C) and N in the areas beneath and between the windrows. Methods. We used conventional chemical methods, anaerobic incubation assay, 13C and 15N natural abundance analyses and, solid-state 13C nuclear magnetic resonance (NMR) spectroscopy. Results. Percent mineralisable N (PCMN) was the only parameter in the underneath windrow position at the Year 1 site that did not show a significant difference to the rest of the positions along the transect. However positions adjacent to windrows did have significantly greater PCMN at the Year 1 site than other positions along the transect. PCMN, total N and total C were significantly greater underneath the windrows at the Year 3 site, whilst δ13C was significantly more negative in the underneath windrow positions. Discussion. PCMN was the most sensitive biological indicator of the changes occurring in the soil due to decomposition of the windrows, with the beneath-windrow position having a significantly higher PCMN than the inter-windrow position (p<.0.001) at the Year 3 site. Isotopic natural abundance for both 13C and was able to detect the influx of labile materials from new residues. Solid-state 13C NMR was able to detect inputs of labile C from the windrows at the Year 1 site, whilst the increase in aromatic C at the Year 3 site was indicative of the more advanced stages of windrow decomposition. Conclusions. Decomposition of windrowed residues had a beneficial effect on soil N and C pools. However, the effect remained localised after 3 years, indicating that trees needed to be planted close to the windrows to gain any benefit from residue decomposition. Recommendations and Perspectives. The use of windrows allows a clear planting area and provides a good barrier against soil erosion. However, trees can only gain access to the nutrients from the decomposing residues if they are planted close to the windrows. Limiting the width of the cleared areas to allow for only 2 planting rows will give the maximum benefit to the developing trees. [ABSTRACT FROM AUTHOR]

Information on decomposition of harvest residues may assist in the maintenance of soil fertility in second rotation (2R) hoop pine plantations (Araucaria cunninghamii Aiton ex A. Cunn.) of subtropical Australia. The experiment was undertaken to determine the dynamics of residue decomposition and fate of residue-derived N. We used 15N-labeled hoop pine foliage, branch, and stem material in microplots, over a 30-mo period following harvesting. We examined the decomposition of each component both singly and combined, and used 13C cross-polarization and magic-angle spinning nuclear magnetic resonance (13C CPMAS NMR) to chart C transformations in decomposing foliage. Residue-derived 15N was immobilized in the 0- to 5-cm soil layer, with approximately 40% 15N recovery in the soil from the combined residues by the end of the 30-mo period. Total recovery of 15N in residues and soil varied between 60 and 80% for the combined-residue microplots, with 20 to 40% of the residue 15N apparently lost. When residues were combined within microplots the rate of foliage decomposition decreased by 30% while the rate of branch and stem decomposition increased by 50 and 40% compared with rates for these components when decomposed separately. Residue decomposition studies should include a combined-residue treatment. Based on 13C CPMAS NMR spectra for decomposing foliage, we obtained good correlations for methoxyl C, aryl C, carbohydrate C and phenolic C with residue mass, 15N enrichment, and total N. The ratio of carbohydrate C to methoxyl C may be useful as an indicator of harvest residue decomposition in hoop pine plantations. [ABSTRACT FROM AUTHOR]

A correction to the article "Effects of weed control and fertilization on soil carbon and nutrient pools in an exotic pine plantation of subtropical Australia," that was published in a previous issue is presented.

Presents abstracts of An abstract of the article "Effect of Overlying Windrowed Harvest Residues on Soil Carbon and Nitrogen in Hoop Pine Plantations of Subtropical Australia," by Timothy J. Blumfield, Zhihong Xu, Nina V. Prasolova, and Nicole J. Mathers.